Copolymerized polyester from phenylene di(oxyaceteic acid) and isophthalic acid

ABSTRACT

Disclosed herein are a coppolymerized polyester produced by copolymerizing a dicarboxylic acid component (A) comprising 
     (a) 10 to 90 mol % of isophthalic acid or an ester forming derivative thereof, 
     (b) 10 to 60 mol % of a phenylenedi(oxyacetic acid) represented by the formula [I]: ##STR1##  (wherein R 1 , R 2 , R 3 , and R 4  each represent a hydrogen atom, an alkyl group having 1 to 6 carbon atom, an alkoxy group having 1 to 6 carbon atom, a phenyl group, a chlorine atom, a bromine atom or a fluorine atom), or as ester forming derivative thereof, and 
     (c) 0 to 45 mol % of a naphthalenedicarboxylic acid or an ester forming derivative thereof, and 
     a diol component (B); and a polyester composition containing the copolymerized polyester.

This a division of application Ser. No. 07/328,517, filed on Mar. 24,1989, now U.S. Pat. No. 4,959,421.

BACKGROUND OF THE INVENTION

The present invention relates to a copolymerized polyester and, moreparticularly, to a copolymerized polyester which is excellent intransparency and gas barrier property, and is useful as a packagingmaterial in the form of a container and a film.

Polyethylene terephthalate which has excellent physical properties suchas mechanical strength, chemical stability, transparency and hygienicquality, and which is light in weight and low in cost, is widely usedfor a container and a film as a packaging material.

However, the gas barrier property of polyethylene terephthalate cannotbe said to be sufficient in some fields, although it is superior tothose of other resins such as polyolefin. For example, a packagingmaterial for carbonated beverage, beer and wine is required to have highoxygen gas barrier property and carbon dioxide gas barrier property inorder to preserve the content, and a generally used hollow container ofbiaxially oriented polyethylene terephthalate cannot satisfy thosestrict conditions on gas barrier properties.

To solve this problem, various methods for improving the gas barrierproperty of a polyethylene terephthalate container have been proposed.For example, (1) a method of labeling a gas barrier material on apolyethylene terephthalate container or coating the polyethyleneterephthalate container with a gas barrier material (Japanese PatentApplication Laid-Open (KOKAI) No. 54-117565 (1979)), (2) a method ofproducing a multi-layered container comprising polyethyleneterephthalate and a gas barrier material (Japanese Patent ApplicationLaid-Open (KOKAI) No. 56-64839 (1981)), and (3) a method of producing acontainer from polyethylene terephthalate with a gas barrier materialblended therewith (Japanese Patent Application Laid-Open (KOKAI) Nos.57-10640 (1982), 59-64658 (1984) and 61-43655 (1986)) have beenproposed.

In the methods (1) and (2), polyvinyliden chloride, a saponifiedethylene-vinyl acetate copolymer, metaxylene diamine nylon, etc. areexemplified as a gas barrier material. These methods, however, aredisadvantageous in the manufacturing process because the step forcoating a container with a gas barrier material is added and a newapparatus for producing a multi-layered container is required. Themethods (1) and (2) are also disadvantageous in that if the adhesionbetween the barrier layer and the polyethylene terephthalate layer ispoor, a ply separation there between is produced.

On the other hand, the method (3) is advantageous in that it is possibleto produce a container having a gas barrier property by utilizingconventional manufacturing apparatus and manufacturing process. However,since a material having a good compatibility with polyethyleneterephthalate and a refractive index approximate to that of polyethyleneterephthalate is necessary in order to maintain the transparency of ablend, a material is not usable as a gas barrier material in the method(3) merely because it has an excellent gas barrier property. Althoughpolyethylene isophthalate and a copolyester thereof have been proposedas a gas barrier material which satisfies the above-describedrequirements, the gas barrier properties thereof are insufficient forimproving the gas barrier property of polyethylene terephthalate.

As a polyester used as a packaging material in place of polyethyleneterephthalate, polyalkylene isophthalate copolymerized with aliphaticdicarboxylic acid having 4 to 12 carbon atoms has been proposed (U.S.Pat. No. 4,403,090), but this polyester is not sufficient for improvingthe gas barrier property of a polyethylene terephthalate packagingmaterial.

Although a polyester produced by copolymerizing phenylene dioxydiaceticacid and polyethylene terephthalate has been proposed (Japanese PatentApplication Laid-Open (KOKAI) No. 60-501060 (1985)), the improvement ofgas barrier property cannot be said to be sufficient.

As a gas barrier material having an excellent ply adhesion, polyesterscontaining isophthalic acid as the main acid component have beenproposed (Japanese Patent Application Laid-Open (KOKAI) Nos. 59-39547(1984), 59-67049 (1984) and 59-89149 (1984)). In these gas barriermaterials disclosed in the above-described specification, however, thebarrier level is low and in order to produce a container having asufficient gas barrier property, it is necessary to make the barrierlayer thick. The total thickness of the container is, therefore,inconveniently increased. Alternatively, if the polyethyleneterephthalate layer is made thin due to the limitation in the totalthickness, the mechanical strength and the heat resistance are impaired.

U.S. Pat. No. 4,663,426 also discloses a polyester resin of a diol and adiacid component comprising about 5 to 50 mole % ofphenylenedioxydiacetic acid and 50 to about 95 mole % ofnaphthalenedicarboxylic acid, and further discloses that otherwell-known polyester-forming diacid such as isophthalic acid,1,4-cyclohexanedicarboxylic acid, linear lower alkyldicarboxylic acidmay be employed. However, this polyester containing a large amount ofnaphthalenedicarboxylic acid has a high glass transition point (Tg) andis fundamentally a rigid polymer. Further, when this polyester is usedas a blend or a laminate with PET, the improvement of the gas barrierproperty of PET is insufficient.

As a result of the study undertaken by the present inventors to solvethe above-described problems in the prior art, it has been found that acopolymerized polyester obtained by copolymerizing a dicarboxylic acidcomponent (A) containing (a) isophthalic acid or an ester formingderivative thereof and (b) a specific phenylenedi(oxyacetic acid) or anester forming derivative thereof in a specified ratio and a diolcomponent (B) is excellent not only in physical properties such asmechanical strength and transparency but also in gas barrier property.On the basis of this finding, the present invention has been achieved.

SUMMARY OF THE INVENTION

In a 1st aspect of the present invention, there is provided acopolymerized polyester produced by copolymerizing a dicarboxylic acidcomponent (A) comprising

(a) 10 to 90 mol % of isophthalic acid or an ester forming derivativethereof,

(b) 10 to 60 mol % of a phenylenedi(oxyacetic acid) represented by theformula [I]: ##STR2## (wherein R¹, R², R³ and R⁴ each represents ahydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxygroup having 1 to 6 carbon atoms, a phenyl group, a chlorine atom, abromine atom or a fluorine atom), or an ester forming derivativethereof, and

(c) 0 to 45 mol % of a naphthalenedicarboxylic acid or an ester formingderivative thereof; and

a diol component (B).

In a 2nd aspect of the present invention, there is provided acopolymerized polyester produced by copolymerizing a dicarboxylic acidcomponent (A) comprising

(a) 40 to 90 mol % of isophthalic acid or an ester forming derivativethereof, and

(b) 10 to 60 mol % of a phenylenedi(oxyacetic acid) represented by theformula [I]: ##STR3## (wherein R¹, R², R³ and R⁴ each represents ahydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxygroup having 1 to 6 carbon atoms, a phenyl group, a chlorine atom, abromine atom or a fluorine atom), or an ester forming derivativethereof, and

a diol component (B).

In a 3rd aspect of the present invention, there is provided acopolymerized polyester produced by copolymerizing a dicarboxylic acidcomponent (A) comprising

(a) 50 to 85 mol % of isophthalic acid or an ester forming derivativethereof,

(b) 10 to 45 mol % of a phenylenedi(oxyacetic acid) represented by theformula [I]: ##STR4## (wherein R¹, R², R³, and R⁴ each represents ahydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxygroup having 1 to 6 carbon atoms, a phenyl group, a chlorine atom, abromine atom or a fluorine atom), or an ester forming derivativethereof, and

(c) 5 to 40 mol % of naphthalenedicarboxylic acid or an ester formingderivative thereof; and

a diol component (B).

In a 4th aspect of the present invention, there is provided acopolymerized polyester produced by copolymerizing a dicarboxylic acidcomponent (A) comprising

(a) 10 to 50 mol % of isophthalic acid or an ester forming derivativethereof,

(b) 20 to 60 mol % of a phenylenedi(oxyacetic acid) represented by theformula [I] ##STR5## (wherein R¹, R², R³ and R⁴ each represents ahydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxygroup having 1 to 6 carbon atoms, a phenyl group, a chlorine atom, abromine atom or a fluorine atom), or an ester forming derivativethereof, and

(c) 10 to 45 mol % of naphthalenedicarboxylic acid or an ester formingderivative thereof,

the molar ratio of said component (b) and said component (c) being 50:50to 80:20; and

a diol component (B).

In a 5th aspect of the present invention, there is provided a polyestercomposition comprising a copolymerized polyester produced bycopolymerizing a dicarboxylic acid component (A) comprising

(a) 10 to 90 mol % of isophthalic acid or an ester forming derivativethereof,

(b) 10 to 60 mol % of a phenylenedi(oxyacetic acid) represented by theformula [I]: ##STR6## (wherein R¹, R², R³ and R⁴ each represents ahydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxygroup having 1 to 6 carbon atoms, a phenyl group, a chlorine atom, abromine atom or a fluorine atom), or an ester forming derivativethereof, and

(c) 0 to 45 mol % of a naphthalenedicarboxylic acid or an ester formingderivative thereof, and a diol component (B); and

a polyester containing polyethylene terephthalate as the main component.

In a 6th aspect of the present invention, there is provided a packagingmaterial, a stretched sheet and a hollow container comprising:

a copolymerized polyester produced by copolymerizing a dicarboxylic acidcomponent (A) comprising

(a) 10 to 90 mol % of isophthalic acid or an ester forming derivativethereof,

(b) 10 to 60 mol % of a phenylenedi(oxyacetic acid) represented by theformula [I]: ##STR7## (wherein R¹, R², R³ and R⁴ each represents ahydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxygroup having 1 to 6 carbon atoms, a phenyl group, a chlorine atom, abromine atom or a fluorine atom), or an ester forming derivativethereof, and

(c) 0 to 45 mol % of a naphthalenedicarboxylic acid or an ester formingderivative thereof, and a diol component (B).

In 7th aspect of the present invention, there is provided a packagingmaterial, a stretched sheet and a hollow container comprising:

a copolymerized polyester produced by copolymerizing a dicarboxylic acidcomponent (A) comprising

(a) 10 to 90 mol % of isophthalic acid or an ester forming derivativethereof,

(b) 10 to 60 mol % of a phenylenedi(oxyacetic acid) represented by theformula [I]: ##STR8## (wherein R¹, R², R³ and R⁴ each represents ahydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxygroup having 1 to 6 carbon atoms, a phenyl group, a chlorine atom, abromine atom or a fluorine atom), or an ester forming derivativethereof, and

(c) 0 to 45 mol % of a naphthalenedicarboxylic acid or an ester formingderivative thereof, and a diol component (B); and

a polyester containing polyethylene terephthalate as the main component.

In an8th aspect of the present invention, there is provided amulti-layered packaging material comprising:

a layer of a copolymerized polyester produced by copolymerizing adicarboxylic acid component (A) comprising

(a) 10 to 90 mol % of isophthalic acid or an ester forming derivativethereof,

(b) 10 to 60 mol % of a phenylenedi(oxyacetic acid) represented by theformula [I]: ##STR9## (wherein R¹, R², R³ and R⁴ each represents ahydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxygroup having 1 to 6 carbon atoms, a phenyl group, a chlorine atom, abromine atom or a fluorine atom), or an ester forming derivativethereof, and

(c) 0 to 45 mol % of a naphthalenedicarboxylic acid or an ester formingderivative thereof, and a diol component (B); and

a polyester layer containing polyethylene terephthalate as the maincomponent.

In a 9th aspect of the present invention, there is provided amulti-layered packaging material comprising:

a polyester composition layer comprising a copolymerized polyesterproduced by copolymerizing a dicarboxylic acid component (A) whichcomprises

(a) 10 to 90 mol % of isophthalic acid or an ester forming derivativethereof,

(b) 10 to 60 mol % of a phenylenedi(oxyacetic acid) represented by theformula [I]: ##STR10## (wherein R¹, R², R³ and R⁴ each represents ahydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxygroup having 1 to 6 carbon atoms, a phenyl group, a chlorine atom, abromine atom or a fluorine atom), or an ester forming derivativethereof, and

(c) 0 to 45 mol % of a naphthalenedicarboxylic acid or an ester formingderivative thereof, and a diol component (B), and

a polyester containing polyethylene terephthalate as the main component;and

a polyester layer containing polyethylene terephthalate as the maincomponent.

DETAILED DESCRIPTION OF THE INVENTION

As examples of a phenylenedi(oxyacetic acid) represented by the formula[I]: ##STR11## (wherein R¹, R², R³ and R⁴ each represents a hydrogenatom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having1 to 6 carbon atoms, a phenyl group, a chlorine atom, a bromine atom ora fluorine atom), 1,2-phenylenedi(oxyacetic acid),1,3-phenylenedi(oxyacetic acid), 1,4-phenylenedi(oxyacetic acid),2-methyl-1,3-phenylenedi(oxyacetic acid),5-methyl-1,3-phenylenedi(oxyacetic acid),4-methyl-1,3-phenylenedi(oxyacetic acid),5-ethyl-1,3-phenylenedi(oxyacetic acid),4-ethyl-1,3-phenylenedi(oxyacetic acid),5-methoxy-1,3-phenylenedi(oxyacetic acid),4-methoxy-1,3-phenylenedi(oxyacetic acid),4-chloro-1,2-phenylenedi(oxyacetic acid) and4-chloro-1,3-phenylenedi(oxyacetic acid) may be exemplified. Amongthese, a derivative of 1,3-phenylenedi(oxyacetic acid) is preferable,and 1,3-phenylenedi(oxyacetic acid) is more preferable.

As a naphthalenedicarboxylic acid in the present invention, any isomerthereof is usable. Especially, 1,4-, 1,5-, 1,8-, 2,3-, 2,6- and2,7-structural isomers are preferable. Among these,2,6-naphthalenedicarboxylic acid is particularly preferable.

Phenylenedicarboxylic acids as the dicarboxylic acid component (A) inthe present invention may be used as a raw material of a copolymerizedpolyester of the present invention either in the form of an acid itselfor in the form of an ester forming derivative such as an acid halide andan ester, in particular, an ester forming derivative such as a loweralkyl ester. Alternatively, an oligomer obtained by reacting aphenylenedi(oxyacetic acid)with a glycol may be used for polymerization.

In a copolymerized polyester of the present invention, it is preferablethat an amount of the phenylenedi(oxyacetic acid) unit (b) derived fromthe phenylenedi(oxyacetic acid) represented by the formula [I] is 10 to60 mol % based on all repeating units of the dicarboxylic acid component(A). If the phenylenedi(oxyacetic acid) unit derived from thephenylenedi(oxyacetic acid)represented by the formula [I] exceeds 60 mol%, the strength and the heat resistance are unfavorably lowered. On theother hand, if the phenylenedi(oxyacetic acid) unit derived from thephenylenedi(oxyacetic acid) represented by the formula [I] is less than10 mol %, the gas barrier property is unfavorably lowered.

In a copolymerized polyester of the present invention, an amount of theisophthalic acid unit (a) derived from the isophthalic acid preferablyis 10 to 90 mol % based on all repeating units of the dicarboxylic acidcomponent (A). If the isophthalic acid unit exceeds 90 mol %, the gasbarrier property is lowered, and if the isophthalic acid unit is lessthan 10 mol %, the glass transition point (Tg) of the copolymerizedester obtained is lowered so much as to make it difficult to dry theresin before molding.

In a copolymerized polyester of the present invention, an amount of thenaphthalenedicarboxylic acid unit (c) derived form thenaphthalenedicarboxylic acid is preferably 0 to 45 mol % based on allrepeating units of the dicarboxylic acid component (A). If thenaphthalenedicarboxylic acid unit exceeds 45 mol %, the gas barrierproperty is lowered.

In a copolymerized polyester of the present invention, it is preferablethat the sum of the acid component units (a), (b) and (c) is at least 55mol %, preferably at least 65 mol %, more preferably at least 80 mol %based on all repeating units of the acid component.

Namely, so long as the content of the acid components (a), (b) and (c)contained satisfies the above-described range, it is possible to useanother dicarboxylic acid or a derivative thereof.

As such a dicarboxylic acid, an aromatic dicarboxylic acid such asterephtalic acid; phthalic acid, 4,4'-biphenyldicarboxylic acid,4,4'-diphenoxyethanedicarboxylic acid, 4,4'-diphenylsulfondicarboxylicacid and the structural isomers thereof, an aliphatic dicarboxylic acidsuch as malonic acid, succinic acid and adipic acid, and an oxy acid anda derivative thereof such as hydroxybenzoic acid, hydroxybenzoate andglycolic acid may be exemplified. Among these, an aromatic dicarboxylicacid such as terephthalic acid, 2,6-naphthalenedicarboxylic acid, and4,4'-diphenylsulfondicarboxylic acid are preferable.

As the diol component (B) for a copolymerized polyester of the presentinvention, ethylene glycol, 1,2-propanediol, 1,3-propanediol,1,4-butanediol, pentamethylene glycol, hexamethylene glycol, neopentylglycol, cyclohexanedimethanol, diethylene glycol, and a derivative of anaromatic dihydroxy compound such as Bisphenol A and Bisphenol S areusable. Among these, ethylene glycol is preferable.

A copolymerized polyester of the present invention may contain apolyfunctional compound such as trimethylolpropane, pentaerythritol,glycerin, trimellitic acid, trimesic acid and pyromellitic acid and amonofunctional compound such as o-benzoylbenzoic acid in the range whichdoes not impair the effect of the present invention. Such apolyfunctional or monofunctional compound is preferably used in therange of not more than 20 mol % of the diol component (B).

Embodiments of a copolymerized polyester according to the presentinvention may be described in the following.

(1) A copolymerized polyester produced by copolymerizing:

a dicarboxylic acid component (A) comprising:

(a) 40 to 90 mol % of isophthalic acid or an ester forming derivativethereof, and

(b) 10 to 60 mol % of a phenylenedi(oxyacetic acid) represented by theformula [I]: ##STR12## (wherein R¹, R², R³ and R⁴ each represent ahydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxygroup having 1 to 6 carbon atoms, a phenyl group, a chlorine atom, abromine atom or a fluorine atom), or an ester forming derivativethereof; and

a diol component (B).

(2) A copolymerized polyester produced by copolymerizing:

a dicarboxylic acid component (A) comprising:

(a) 50 to 85 mol % of isophthalic acid or an ester forming derivativethereof,

(b) 10 to 45 mol % of a phenylenedi(oxyacetic acid) represented by theformula [I]: ##STR13## (wherein R¹, R², R³ and R⁴ each represent ahydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxygroup having 1 to 6 carbon atoms, a phenyl group, a chlorine atom, abromine atom or a fluorine atom), or an ester forming derivativethereof, and

(c) 5 to 40 mol % of naphthalenedicarboxylic acid or an ester formingderivative thereof; and

a diol component (B).

(3) A copolymerized polyester produced by copolymerizing;

a dicarboxylic acid component (A) comprising:

(a) 10 to 50 mol % of isophthalic acid or an ester forming derivativethereof,

(b) 20 to 60 mol % of a phenylenedi(oxyacetic acid) represented by thefomula [I]: ##STR14## (wherein R¹, R², R³ and R⁴ each represent ahydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxygroup having 1 to 6 carbon atoms, a phenyl group, a chlorine atom, abromine atom or a fluorine atom), or an ester forming derivativethereof, and

(c) 10 to 45 mol % of naphthalenedicarboxylic acid or an ester formingderivative thereof, wherein the molar ratio of the component (b) and thecomponent (c) is in the range of 50:50 to 80:20; and

a diol component (B).

A copolymerized polyester of the present invention preferably has anintrinsic viscosity of 0.4 to 2.0, preferably 0.50 to 1.2 [measured at30° C. by using a mixed solvent of phenol and tetrachloroethane (in aweight ratio of 1:1)]. If the intrinsic viscosity is less than 0.4, thestrength of the polyester obtained is so low that it is impossible toobtain practically necessary physical properties when the polyester istaken out of the reaction vessel after polymerization and cut intochips, or molded into a container such as a bottle, barrel and can byblending with polyethylene terephthalate or laminating on polyethyleneterephthalate. On the other hand, if the intrinsic viscosity exceeds2.0, the melting viscosity becomes so high as to make molding such asinjection, extrusion or blowing difficult.

The glass transition point (Tg) of a copolymerized polyester of thepresent invention is preferably not lower than 35° C., more preferably50° to 120° C. and the oxygen permeability thereof is preferably notmore than 0.7 cc·mm/m² ·day·atm, more preferably not morethan0.4cc·mm/m² ·day·atm.

A copolymerized polyester of the present invention can be produced byany polymerization method which is conventionally known as apolymerization method for polyethylene terephthalate. For example, apolycondensation method may be adopted, which the method comprises thesteps of directly esterifying isophthalic acid, naphthalenedicarboxylicacid, a phenylenedi(oxyacetic acid)represented by the formula [I] suchas 1,3-phenylenedi(oxyacetic acid) and ethylene glycol under a pressureand thereafter gradually reducing the pressure while raising thetemperature to polycondense the reaction product. It is also possible toproduce a copolymerized polyester of the present invention by subjectingan ester derivative of isophthalic acid such as a dimethyl isophthalate,an ester derivative of naphthalenedicarboxylic acid such as dimethylnaphthalenedicarboxylate, an ester derivative of a phenylenedi(oxyaceticacid represented by the general formula [I] such as diethyl1,3-phenylenedi(oxyacetate) and ethylene glycol to an ester exchangereaction, and further polycondensing the reaction product.

In the production of such a polymer, it is preferable to use anesterifying catalyst, ester exchanging catalyst, polycondensingcatalyst, stabilizer, etc.

As the ester exchanging catalyst, at least one known compound selectedfrom calcium, manganese, zinc, sodium and lithium compounds is usable.Form the point of view of transparency, a manganese compound is morepreferable. As the polycondensing catalyst, at least one known compoundselected from antimony, germanium, titanium and cobalt compounds isusable. Antimony, germanium and titanium compounds are preferably used.

A conventionally known additive such as an antioxidant, ultravioletabsorber, fluorescent brightener, mold release agent, antistatic agent,dispersant and coloring agent such as a dye and a pigment may be added,if necessary, to a polyester in the present invention at anymanufacturing stage. Alternatively, such an additive may be added beforemolding by what is called master batching.

A copolymerized polyester of the present invention may be subjected toheat treatment, if necessary, before use so as to reduce acetaldehyde orlower the oligomerization degree. Alternatively, a copolymerizedpolyester of the present invention may also be subjected to solid-statepolymerization before use so as to enhance the polymerization degree,reduce acetaldehyde or lower the oligomerization degree.

The heat treatment is ordinarily preferably carried out at 30° C. to atemperature directly below the melting point, for several to severalhundred hours. The solid-state polymerization is ordinarily preferablycarried out at 120° C. to a temperature directly below the meltingpoint, preferably 140° to 230° C. for less than several ten hourspreferably 5 to 30 hours after the surfaces of the chips arecrystallized at a temperature of 80° to 180° C.

The thus obtained copolymerized polyester of the present invention ismelted and molded to obtain a product (article).

In order to produce a hollow molded product of the copolymerizedpolyester of the present invention, for example, a blow molding methodsuch as a hot parison process or a cold parison process is adopted inwhich a preform is first produced by ordinary extrusion blow molding,injection blow molding, injection molding or extrusion molding, and thethus obtained preform is reheated and biaxially stretched as it is orafter processing the mouth portion and the bottom portion.

It is also possible to form a uniaxially or biaxially stretched filmfrom a copolymerized polyester of the present invention or a can-shapedcontainer, a tray or the like by vacuum forming or air-pressure formingafter it is formed into a sheet by injection molding. It is alsopossible to form a copolymerized polyester of the present invention intoa multi-layered sheet of the polyester and polyethylene terephthalate,for example, by a multi-layer extruder and thereafter form the sheetinto a uniaxially or biaxially stretched film, a can-shaped container ora tray.

It is further possible to blend a copolymerized polyester of the presentinvention with another thermoplastic resin composition such aspolyethylene terephthalate, polybutylene terephthalate, polyethylenenaphthalate, polyester elastomer, polycarbonate and polyamide so as toform an integral structure product. It is also possible to form amulti-layer structure product by using a copolymerized polyester of thepresent invention, a polyethylene terephthalate component or theabove-described thermoplastic resin component.

As a blend, a composition of 5 to 80 wt. % of a copolymerized polyesterof the present invention and 20 to 95 wt. % of another thermoplasticresin composition such as polyethylene terephthalate is preferable.

If the content of a polymerized polyester is less than 5 wt. %, theimprovement of the gas barrier property of polyethylene terephthalate issometimes insufficient. If the content exceeds 80 wt. %, the improvingeffect is sometimes lowered in the respects of mechanical strength andheat resistance.

A polyester composition according to the present invention also ismelted, and molded into a molded product (article). For example, acopolymerized polyester may be blended with polyethylene terephthalate,melted and kneaded by an extruder so as to obtain mixed chips and themixed chips are molded. Alternatively, each of the components is dryblended and directly supplied to a molding process.

If the melting point and glass transition point of the copolymerizedpolyester of the present invention lower, the troubles such as fusingetc. are easily caused depending on the composition of the comonomersthereof and as a result the operating property tends to deteriorate.Accordingly, in the case where the copolymerized polyester of thepresent invention is used in the form of a blend with a base resin suchas polybutylene terephthalate, polyethylene naphthalate, polyesterelastomer, polycarbonate, polyamide etc., after previously mixing thecopolymerized polyester of the present invention with the base resin andsubjecting a mixture to heat treatment and/or solid-state polymerizationso as to reduce acetaldehyde and lower the content of oligomer, the thusobtained blend is preferably used. These heat treatment and solid-statepolymerization is ordinarily carried out at 30° C. to a temperaturedirectly below the melting point of the base resin, preferably 100° to300° C.

A polyester composition of the present invention can be formed into afilm, sheet, container, and other packaging material by a melt moldingmethod which is generally used in molding polyethylene terephthalate.The polyester composition is usable as a material having a high gasbarrier property in an unstretched state. By stretching the polyestercomposition at least uniaxially, it is possible to improve the gasbarrier property and the mechanical strength.

A stretched sheet of a polyester composition of the present invention isproduced by stretching a polyester composition of the present inventionwhich has been formed into a sheet by injection molding or extrusionmolding. The stretching method adopted may be freely selected fromuniaxially stretching, sequential biaxially stretching and simultaneousbiaxially stretching. It is also possible to form a stretched sheet of apolyester composition of the present invention into a cup or a tray byair-pressure forming.

When a stretched sheet of a polyester composition of the presentinvention is produced, the stretching temperature is set between theglass transition point (Tg) of the polyester and a temperature 70° C.higher than the glass transition point (Tg) as in the case of producinga stretched sheet of a copolymerized polyester of the present invention.The stretching ratio is ordinarily 1.1 to 10 times, preferably 1.1 to 8times in the case of uniaxial stretching, and 1.1 to 8 times, preferably1.1 to 5 times in both machine and transverse directions in the case ofbiaxial stretching. The thus obtained stretched sheet of a polyestercomposition of the present invention is excellent in transparency, gasbarrier property and mechanical strength and is useful as a packagingmaterial in the form of a film, a cup or a tray.

A polyester hollow molded product of the present invention is producedby stretching and blowing the preform produced from a copolymerizedpolyester or a polyester composition of the present invention. It is,therefore, possible to use an apparatus conventionally used in the blowmolding of polyethylene terephthalate. More specifically, a blow moldingmethod such as a hot parison process or a cold parison process isadopted in which a preform is first produced by ordinary extrusion blowmolding, injection blow molding, injection molding or extrusion molding,and the thus obtained preform is reheated and biaxially stretched as itis or after processing the mouth portion and the bottom portion. Thestretching temperature is 70° to 120° C., preferably 80° to 110° C., andthe stretching ratio is 1.5 to 3.5 times in the machine direction and 2to 5 times in the circumferential direction.

When a polyester hollow molded product is produced, it is possible tofirst form a preform of a laminate comprising a layer of a copolymerizedpolyester or polyester composition of the present invention and a layerof polyalkylene terephthalate mainly containing polyethyleneterephthalate, and to biaxially blow the thus obtained preform in orderto produce a multi-layered hollow container. In this case, the structureof the multilayer is not restricted, but a multilayer of three to fivelayers is preferable.

Especially, a multi-layered structure of at least one copolymerizedpolyester or polyester composition of the present invention and at leastone polyester layer containing polyethylene terephthalate as the maincomponent (hereinafter referred to merely as "polyester layer") ispreferable.

The polyester of the polyester layer in the present invention meanspolyethylene terephthalate and a nonthermal liquid crystal polyestercontaining polyethylene terephthalate as the main component. It ispreferable that at least 80 mol % of the structural unit of thepolyester is ethylene terephthalate units, and it is possible to use adicarboxylic acid such as phthalic acid, isophthalic acid,hexahydrophthalic acid, naphthalenedicarboxylic acid, succinic acid,adipic acid and sebacic acid and a polyfunctional carboxylic acid suchas trimellitic acid and pyromellitic acid as an acid component in therange of at most 20 mol % of the total acid component.

It is possible to use a glycol such as 1,2-propanediol, 1,3-propanediol,1,4-butanediol, 1,6-hexanediol, neopentyl glycol, diethylene glycol,triethylene glycol and cyclohexanedimethanol, and a polyvalent alcoholsuch as trimethylolpropane, triethylolpropane and pentaerythritol in therange of not exceeding 20 mol % of the total alcohol component.

The intrinsic viscosity of the polyester containing polyethyleneterephthalate as the main component is preferably 0.6 to 1.2 [measuredat 30° C. by using a mixed solvent of phenol and tetrachloroethane (in aweight ratio of 1:1)], and the glass transition point (Tg) thereof ispreferably 70° to 72° C.

The polyester may be blended with another polyester and used as apolyester layer. In this case, the content of polyethylene terephthalatein the polyester layer is preferably not less than 50%.

The polyester containing polyethylene terephthalate as the maincomponent can be produced by a known polymerization method as in thecopolymerized polyester of the present invention. The polyester may besubjected to solid-state polymerization, if necessary. The solid-statepolymerization is ordinarily carried out at 170° C. to a temperaturedirectly below the melting point of the polyester, preferably 183° to230° C. for less than several ten hours, preferably not less than 5hours.

A multi-layered polyester hollow container according to the presentinvention is produced by forming a preform of a multi-layered hollowcontainer from a copolymerized polyester or polyester composition and apolyester containing polyethylene terephthalate as the main componentwhich are obtained in the above-described method, and stretching thethus obtained preform at a temperature above the glass transition point(Tg) of the polyester layer at least in the biaxial direction. Themultilayer may be composed of either two layers or not less than threelayers. A multilayer of three to five layers is preferable. In thiscase, it is preferable that the innermost layer of the hollow containeris a polyester layer. This is because the copolymerized polyester andpolyester composition have slightly more low-molecular weight componentsthan polyethylene terephthalate, so that it is unfavorable that thecopolymerized polyester and polyester composition are in direct contactwith the content. The outermost layer of the hollow container may beeither the copolymerized polyester, polyester composition orpolyethylene terephthalate, but polyethylene terephthalate is preferablein terms of surface strength. When the outermost layer is composed ofthe copolymerized polyester or polyester composition, a protective layermay be provided on the outside of the outermost layer for the purpose ofprotecting the surface. The protective layer may be formed at a stagefor forming the preform of the hollow container. Alternatively, theprotective layer may be formed after the preform is stretched so as toproduce the hollow container by labelling or the like.

The thickness of the polyester layer and the thickness of thecopolymerized polyester layer are not specified. Generally, the totalthickness of the bottle body is 200 to 700μ, preferably 250 to 600μ. Thethickness of the copolymerized polyester or polyester composition layeris different depending upon the desired barrier property, but it isgenerally 5 to 300μ, preferably 10 to 200μ.

A container of the present invention is produced by extrusion blowmolding or biaxial orientation blow molding which is conventionallyknown. Biaxial orientation blow molding is more advantageous. In thecase of using biaxial orientation blow molding, the preform of thehollow container is formed, and after the preform is heated to thestretching temperature, it is stretched within a blow mold.

In order to form a preform of the hollow container having a multi-layerstructure, a bottomed preform may be formed by injection molding, orafter a multi-layered pipe is formed, one end thereof may be formed intoa bottom. When a preform of a hollow container having a multi-layerstructure or a multi-layered pipe is produced, the layers may be formedsequentially from the innermost layer by an ordinary injection moldingmachine or a molding machine having a plurality of melt injectionapparatuses, or the respective layers may be extruded from a pluralityof injecting apparatuses into a single mold one by one, so that thepolyethylene terephthalate resin injected first may constitute theinnermost layer and the outermost layer and the copolymerized polyesteror polyester composition injected later constitutes an intermediatelayer. By selecting the injection timing, it is possible to design thepreform so as to have three layers, five layers or more.

The preform of the hollow container obtained is generally heated in aheating zone having a heater such as a block heater and an infraredheater for the subsequent stretching process. The heating temperaturefor the preform for a polyester multi-layered hollow container of thepresent invention is determined by the glass transition temperature(hereinunder referred to as "Tg(1)") of the polyester layer and theglass transition temperature (hereinunder referred to as "Tg(2)") of thecopolymerized polyester or polyester composition layer. The heatingtemperature is at least not lower than Tg(1), and preferably in therange of Tg(1)+5° C. to Tg (2)+80° C. If the heating temperature is toolow, micro voids are produced due to cold stretching and the containerunfavorably presents the pearl or foggy appearance. On the other hand,if the heating temperature is too high, the perform becomes too soft toobtain a hollow container having a sufficient stretching effect.

When the preform of a polyester multi-layered hollow container isstretched to form the hollow container, the preform is preferablystretched by 1 to 4 times in the machine direction and by 2 to 6 timesin the transverse direction (circumferential direction of the container)by moving a rod in the machine direction and blowing pressurized air. Inorder to enhance the heat resistance of the container, it is possible toheat set the container by further heating the stretched hollow containerwithin the mold at a temperature the same as or higher than thestretching temperature for a short time. In manufacturing a polyestermulti-layered hollow container of the present invention, it is possibleto blend other polyesters such as polyethylene terephthalate with thecopolymerized polyester or polyester composition layer. In this case,the content of the copolymerized polyester in the layer is not less than10 wt. %, preferably not less than 30 wt. %.

In such a polyester packaging material, a copolymerized polyestercomponent of the present invention preferably exists in the range of 2to 30 mol % of the total polyesters in terms of thephenylenedi(oxyacetic acid)unit represented by the general formula [I].If the copolymerized polyester component exceeds 30 mol %, the gasbarrier improving effect is sometimes not so prominent and the moldedproduct cannot sometimes retain the practical physical properties. Ifthe copolymerized polyester component is less than 2 mol %, the gasbarrier improving effect is sometimes not prominent, either.

The copolymerized polyester or polyester composition of the presentinvention itself exhibits a high transparency and has an excellent gasbarrier property. The copolymerized polyester on polyester compositionof the present invention is useful as a packaging material and can alsobe widely used as a container, sheet, film, etc. in the form of a blendor a laminate with other thermoplastic resins.

Particularly, a blend or a laminate of the copolymerized polyester ofthe present invention with polyethylene terephthalate has a low gaspermeability while retaining a high transparency, so that it can beutilized very advantageously. Such a blend or a laminate can also beused together with a gas barrier material such as vinylidene chloride ora saponified ethylene-vinyl acetate copolymer.

A polyester hollow molded product of the present invention, which has ahigh mechanical strength as well as excellent transparency and gasbarrier property, can be widely used for fresh beverage, flavoringmaterial, oil, alcoholic drink such as beer, wine and sake, andcosmetics. Particularly, the polyester hollow molded product of thepresent invention can be used as a small-sized container for carbonateddrink, beer, wine or the like, which would not be preserved for apredetermined guaranteed period due to the insufficient gas barrierproperty by an ordinary biaxially stretched polyethylene terephthalatebottle.

Especially, a polyester multi-layered hollow container of the presentinvention has an excellent gas barrier property, a high mechanicalstrength free from ply separation and an excellent transparency in theexternal appearance. A polyester multi-layered hollow container of thepresent invention can therefore be widely used for fresh beverage,flavoring material, oil, alcoholic drink such as beer, wine and sake,and cosmetics.

The present invention will be explained in more detail with reference tothe following non-limitative examples.

EXAMPLES

"Part" in the examples means "part by weight". The physical propertieswere measured in the following manners.

Intrinsic viscosity (deciliter/gram)

Intrinsic viscosity was measured at 30° C. in a mixed solvent ofphenol-tetrachloroethane (weight ratio: 50:50).

Oxygen permeability

An extruded sheet sample of about 200 μm thick and a stretched bottle ofabout 200 μm thick were produced. The oxygen permeability was measuredat 23° C. and 100% RH by an oxygen permeability measuring apparatusOX-TRAN 10/50 (produced by Modern Controls, USA) and expressed bycc·mm/m² ·day·atm or cc/bottle·day·atm.

EXAMPLE 1

16,000 parts of isophthalic acid and 7,100 parts of ethylene glycol werecharged into an autoclave and were subjected to esterification reactionat 220° to 245° C. for 3 hours under a pressure of 2.5 kg/cm² in anitrogen atmosphere under stirring, while distilling off the waterproduced during the reaction to the outside of the system.

To the esterified product, 2,400 parts of 1,3-phenylenedi(oxyaceticacid) and 16 parts of titanium tetrabutoxide were added. The pressure ofthe polymerizer was gradually reduced from ordinary pressure to 1 Torrand the temperature was gradually raised to 260° C., and after 5-hourpolymerization in total, a transparent polyester having an intrinsicviscosity of 0.70 was obtained.

EXAMPLE 2

15,500 parts of dimethylisophthalate, 10,500 parts of ethylene glycoland 4 parts of manganese acetate tetrahydrate were charged into areaction vessel and were subjected to ester exchange reaction whilegradually raising the temperature from 160° C. to 230° C. until therewas no effluent.

To the reaction system, 4,500 parts of 1,3-phenylenedi(oxyacetic acid),2.6 parts of orthophosphoric acid and 2.0 parts of germanium dioxidewere added. The pressure of the polymerizer was gradually reduced fromordinary pressure to 1 Torr and the temperature was gradually raisedfrom 230° C. to 260° C., and after 4.5-hour polymerization in total, ahighly transparent polyester having an intrinsic viscosity of 0.67 wasobtained.

EXAMPLE 3

Polymerization was carried out in the same way as in Example 1 exceptthat 12,000 parts of isophthalic acid and 7,000 parts of1,3-phenylenedi(oxyacetic acid) were used. The intrinsic viscosity ofthe polymer obtained was 0.72.

EXAMPLE 4

Polymerization was carried out in the same way as in Example 1 exceptthat 10,000 parts of isophthalic acid and 9,200 parts of1,3-phenylenedi(oxyacetic acid) were used. The intrinsic viscosity ofthe polymer obtained was 0.68.

EXAMPLE 5

Polymerization was carried out in the same way as in Example 1 exceptthat 6,000 parts of isophthalic acid and 12,000 parts of1,3-phenylenedi(oxyacetic acid) were used. The intrinsic viscosity ofthe polymer obtained was 0.72.

EXAMPLE 6

Polymerization was carried out in the same way as in Example 1 exceptthat 14,000 parts of isophthalic acid and 4,800 parts of1,2-phenylenedi(oxyacetic acid) in place of 1,3-phenylenedi(oxyaceticacid) were used. The intrinsic viscosity of the polymer obtained was0.70.

EXAMPLE 7

Polymerization was carried out in the same way as in Example 1 exceptthat 14,000 parts of isophthalic acid and 4,800 parts of1,4-phenylenedi(oxyacetic acid) in place of 1,3-phenylenedi(oxyaceticacid) were used. The intrinsic viscosity of the polymer obtained was0.72.

COMPARATIVE EXAMPLE 1

18,000 parts of isophthalic acid and 8,000 parts of ethylene glycol werecharged into an autoclave and were subjected to esterification reactionat 220° to 245° C. for 3 hours under a pressure of 2.5 kg/cm² in anitrogen atmosphere under stirring, while distilling off the waterproduced during the reaction to the outside of the system.

To the esterified product, 18 parts of titanium tetrabutoxide wereadded. The pressure of the polymerizer was gradually reduced fromordinary pressure to 1 Torr and the temperature was gradually raised to270° C., and after 4-hour polymerization in total, a highly transparentpolyester having an intrinsic viscosity of 0.70 was obtained.

COMPARATIVE EXAMPLE 2

Polymerization was carried out in the same way as in Example 2 exceptthat 15,500 parts of dimethylterephthalate were used in place ofdimethylisophthalate. The intrinsic viscosity of the polymer obtainedwas 0.69.

COMPARATIVE EXAMPLE 3

18,000 parts of 1,3-phenylenedi(oxyacetic acid) and 5,500 parts ofethylene glycol were charged into an autoclave and were subjected toesterification reaction at 220° to 245° C. for 3 hours under a pressureof 2.5 kg/cm² in a nitrogen atmosphere under stirring, while distillingoff the water produced during the reaction to the outside of the system.

To the esterified product, 18 parts of titanium tetrabutoxide wereadded. The pressure of the polymerizer was gradually reduced fromordinary pressure to 1 Torr and the temperature was gradually raised to260° C., and after 3-hour polymerization in total, a highly transparentpolyester having an intrinsic viscosity of 0.65 was obtained.

The polymer obtained was dried at 30° to 35° C. by a vacuum drier butthe pellets were fused and difficult to use.

The polyester resins obtained in Examples 1 to 5 and ComparativeExamples 1 and 2 were extruded into sheets of about 200 μm thick and theoxygen permeabilities thereof were measured. The results are shown inTable 1.

                                      TABLE 1                                     __________________________________________________________________________           Acid component                                                                                      A/B                                                                           (Molar                                                                             Oxygen permeability                                Component (A)                                                                            Component (B)                                                                            ratio)                                                                             (cc · mm/m.sup.2 ·                                          day · atm)                         __________________________________________________________________________    Example 1                                                                            Isophthalic acid                                                                         1,3-       90/10                                                                              0.61                                                          Phenylenedi(oxyacetic                                                         acid)                                                       Example 2                                                                            Dimethylisophthalate                                                                     1,3-       80/20                                                                              0.35                                                          Phenylenedi(oxyacetic                                                         acid)                                                       Example 3                                                                            Isophthalic acid                                                                         1,3-       70/30                                                                              0.22                                                          Phenylenedi(oxyacetic                                                         acid)                                                       Example 4                                                                              "        1,3-       60/40                                                                              0.16                                                          Phenylenedi(oxyacetic                                                         acid)                                                       Example 5                                                                              "        1,3-       40/60                                                                              0.12                                                          Phenylenedi(oxyacetic                                                         acid)                                                       Example 6                                                                              "        1,2-       80/20                                                                              0.37                                                          Phenylenedi(oxyacetic                                                         acid)                                                       Example 7                                                                              "        1,4-       "    0.58                                                          Phenylenedi(oxyacetic                                                         acid)                                                       Comparative                                                                            "          --       100/0                                                                              0.72                                        Example 1                                                                     Comparative                                                                          Dimethylterephthalate                                                                    1,3-       80/20                                                                              0.98                                        Example 2         Phenylenedi(oxyacetic                                                         acid)                                                       __________________________________________________________________________

It is clear from Table 1 that a polymer containing a predeterminedamount of phenylenedicarboxilic acid represented by the general formula(I) has a smaller gas permeability than polyethylene terephthalate and acopolymer of polyethylene terephthalate and phenylenedi(oxyacetic acid)and that such a polymer is suitable as a packaging material having ahigh gas barrier property.

EXAMPLE 8

38 parts of dimethylisophthalate, 48 parts of dimethylnaphthalenedicarboxylate, 48 parts of ethylene glycol and 0.03 part of manganeseacetate tetrahydrate were charged into a reaction vessel and weresubjected to easter exchange reaction while gradually raising thetemperature from 160° C. to 230° C. until there was no effluent.

To the reaction system, 59 parts of 1,3-phenylenedi(oxyacetic acid),0.02 part of orthophosphoric acid and 0.03 part of germanium dioxidewere added in that order. The pressure of the polymerizer was graduallyreduced from ordinary pressure to 0.5 Torr and the temperature wasgradually raised from 230° C. to 260° C., and after 6-hourpolymerization in total, a highly transparent polyester having anintrinsic viscosity of 0.71 was obtained.

EXAMPLE 9

Polymerization was carried out in the same way as in Example 8 exceptthat 52 parts of dimethylisophthalate, 30 parts of1,3-phenylenedi(oxyacetic acid), 65 parts of dimethylnaphthalenedicrboxylate and 66 parts of ethylene glycol were used. The intrinsicviscosity of the polymer obtained was 0.69.

EXAMPLE 10

51 parts of dimethylisophthalate, 89 parts of 1,3-phenylenedi(oxyaceticacid), 33 parts of ethylene glycol and 0.03 part of titaniumtetrabutoxide were charged into a reaction vessel and were subjected toester exchange reaction while gradually raising the temperature from200° C. to 230° C. until there was no effluent.

The pressure of the polymerizer was gradually reduced from ordinarypressure to 1 Torr and the temperature was gradually raised from 230° C.to 260° C., and after 5.0-hour polymerization in total, a highlytransparent polyester having an intrinsic viscosity of 0.65 wasobtained.

EXAMPLE 11

Polymerization was carried out in the same way as in Example 8 exceptthat 82 parts of dimethylisophthalate, 32 parts of1,3-phenylenedi(oxyacetic acid), 34 parts of dimethylnaphthalenedicarboxylate and 70 parts of ethylene glycol were used. The intrinsicviscosity of the polymer obtained was 0.70.

EXAMPLE 12

Polymerization was carried out in the same way as in Example 8 exceptthat 114 parts of dimethylisophthalate, 33 parts of1,3-phenylenedi(oxyacetic acid), 0 part of dimethylnaphthalenedicarboxylate and 73 parts of ethylene glycol were used. The intrinsicviscosity of the polymer obtained was 0.68.

EXAMPLE 13

Polymerization was carried out in the same way as in Example 8 exceptthat 25 parts of dimethylisophthalate, 52 parts of1,3-phenylenedi(oxyacetic acid), 72 parts of 2,6-dimethylnaphthalenedicarboxylate and 48 parts of ethylene glycol were used. The intrinsicviscosity of the polymer obtained was 0.70.

EXAMPLE 14

Polymerization was carried out in the same way as in Example 8 exceptthat 13 parts of dimethylisophthalate, 75 parts of1,3-phenylenedi(oxyacetic acid), 65 parts of 2,6-dimethylnapthalenedicarboxylate and 66 parts of ethylene glycol were used. The intrinsicviscosity of the polymer obtained was 0.68.

EXAMPLE 15

Polymerization was carried out in the same way as in Example 8 exceptthat 29 parts of dimethylisophthalate, 83 parts of1,3-phenylenedi(oxyacetic acid), 54 parts of 2,6-dimethylnaphthalenedicarboxylate and 73 parts of ethylene glycol were used. The intrinsicviscosity of the polymer obtained was 0.70.

COMPARATIVE EXAMPLE 4

Polymerization was carried out in the same way as in Example 8 exceptthat 152 parts of dimethylisophthalate and 97 parts of ethylene glycolwere used. The intrinsic viscosity of the polymer obtained was 0.73.

The copolymerized polyesters obtained in Examples 8 to 12 andComparative Example 4 were pressed into sheets of about 200 μm thick andthe oxygen permeabilities thereof were measured. The results arecollectively shown in Table 2.

                  TABLE 2                                                         ______________________________________                                        Examples of Copolymerized Polyester                                                                                In-                                      Dicarboxylic acid                    trinsic                                  (Mol % in acid component)     Tg     Vis-                                     IPA.sup.(1) PDDA.sup.(2)                                                                           NDCA.sup.(3)                                                                           PO.sub.2.sup.(4)                                                                    (°C.)                                                                       cosity                               ______________________________________                                        Example 8                                                                             30      40       30     0.25  53   0.71                               Example 9                                                                             40      20       40     0.48  66   0.69                               Example 10                                                                            40      60        0     0.11  39   0.65                               Example 11                                                                            60      20       20     0.43  56   0.70                               Example 12                                                                            80      20        0     0.30  48   0.68                               Example 13                                                                            20      35       45     0.30  60   0.70                               Example 14                                                                            10      50       40     0.14  53   0.68                               Example 15                                                                            20      50       30     0.12  51   0.70                               Com-    100      0        0     0.78  60   0.73                               parative                                                                      Example 4                                                                     ______________________________________                                         [Notes                                                                        .sup.(1) IPA: isophthalic acid                                                .sup.(2) PDDA: 1,3phenylenedi(oxyacetic acid)                                 .sup.(3) NDCA: 2,6naphthalenedicarboxylic acid                                .sup.(4) PO.sub.2 : oxygen permeability, cc · mm/m.sup.2             · day · atm.                                           

EXAMPLES 16 and 17

The copolymerized polyesters obtained in Example 8 and 9 were melted andblended with a polyethylene terephthalate (RT 543C, produced by NihonUnipet K.K.) having an intrinsic viscosity of 0.75 in the ratios shownin Table 3 and the blends were pressed into sheets of about 200 μmthick. The oxygen permeabilities thereof were measured. The results areshown in Table 3.

EXAMPLES 18-20 and 21

The copolymerized polyester obtained in Examples 8, 9, 13 and 14 wererespectively blended with a polyethylene terephthalate (RT 543C,produced by Nihon Unipet K.K.) in the state of pellets in the ratiosshown in Table 3 and the blends were formed into flat plates of 6 cm×6cm by injection molding (by Nikko 0.80 z Injection machine). The flatplates were simultaneously stretched by 3 times in the machine andtransverse directions by a Long stretching machine to obtain stretchedsheets of about 100 μm thick. The oxygen permeabilities thereof weremeasured. The results are collectively shown in Table 3.

COMPARATIVE EXAMPLES 5 and 6

The oxygen permeability of a polyethylene terephthalate (RT 543C,produced by Nihon Unipet K.K.) was measured in the form of anunstretched film in the same way as in Examples 8 and 9. The oxygenpermeability thereof was also measured in the form of a stretched filmin the same way as in Examples 15 and 16. The results are shown in Table3.

COMPARATIVE EXAMPLES 7 and 8

The polyethylene isophthalate obtained in Comparative Example 4 wasblended with a polyethylene terephthalate in the same way as in Examples8 and 9, and the oxygen permeability of the unstretched film wasmeasured. The polyethylene isophthalate was also blended with apolyethylene terephthalate and the blend was stretched in the same wayas in Examples 18 and 19 to obtain a stretched film. The oxygenpermeability thereof was measured. The results are shown in Table 3.

                  TABLE 3                                                         ______________________________________                                        Oxygen Permeability of Polyester Composition.sup.(1)                                 Copolymerized        Mixing.sup.(3)                                           Polyester Stretching.sup.(2)                                                                       amount                                                   produced in                                                                             condition  (wt %)   PO.sub.2.sup.(4)                         ______________________________________                                        Example 16                                                                             Example 8   Unstretched                                                                              20     1.9                                    Example 17                                                                             Example 9   Unstretched                                                                              30     2.0                                    Example 18                                                                             Example 8   3 × 3                                                                               5     1.5                                                                    20     0.85                                                                   40     0.56                                   Example 19                                                                             Example 9   3 × 3                                                                              10     1.6                                                                    30     1.1                                                                    60     0.78                                   Example 20                                                                             Example 13  3 × 3                                                                               5     1.2                                                                    20     0.74                                   Example 21                                                                             Example 14  3 × 3                                                                              10     0.60                                                                   20     0.48                                   Comparative                                                                             --         Unstretched                                                                               0     3.6                                    Example 5                                                                     Comparative                                                                             --         3 × 3                                                                               0     2.3                                    Example 6                                                                     Comparative                                                                            Comparative Unstretched                                                                              20     2.7                                    Example 7                                                                              Example 4                                                            Comparative                                                                            Comparative 3 × 3                                                                              20     1.7                                    Example 8                                                                              Example 4                                                            ______________________________________                                         [Notes                                                                        .sup.(1) Polyester composition: blend of polyethylene terephthalate (RT       543C, produced by Nihon Unipet K.K.) and copolymerized polyester              .sup.(2) Stretching conditions:                                               Stretching temperature: 98°  C., simultaneous biaxial stretching       .sup.(3) Mixing amount: content of copolymerized polyester in the             polyester composition                                                         .sup.(4) PO.sub.2 : Oxygen permeability, cc.mm/m.sup.2.day.atm.          

EXAMPLE 22

10 parts of the copolymerized polyester obtained in Example 8 were dryblended with 90 parts of a polyethylene terephthalate (RT 543C, producedby Nihon Unipet K.K.), and the blend was formed into a preform for abottle by injection molding. The preform was formed into a stretchedbottle having an inner volume of 1.5 l by a biaxial orientation blowingmachine. The average wall thickness of the shoulder portion and the bodyportion was 0.33 mm and the total surface area was 700 cm². The oxygenpermeability of the bottle obtained was measured 0.21 cc/bottle·day·atm.

EXAMPLE 23

20 parts of the copolymerized polyester obtained in Example 13 were dryblended with 80 parts of a polyethylene terephthalate (RT543C, producedby Nihon Unipet K.K.), and the blend was formed into a preform for abottle by injection molding. The preform was formed into a stretchedbottle having an inner volume of 1.5 l by a biaxial orientation blowingmachine. The average wall thickness of the shoulder portion and the bodyportion was 0.33 mm and the total surface area was 700 cm². The oxygenpermeability of the bottle obtained was measured 0.21 cc/bottle·day·atm.

COMPARATIVE EXAMPLE 9

A stretched bottle having an inner volume of 1.5 l was formed by using apolyethylene terephthalate (RT 543C, produced by Nihon Unipet K.K.)solely in the same way as in Example 22. The oxygen permeability of thebottle obtained was measured 0.43 cc/bottle·day·atm.

COMPARATIVE EXAMPLE 10

A stretched bottle having an inner volume of 1.5 l was formed by using10 parts of the polyethylene isophthalate obtained in ComparativeExample 4 and 90 parts of a polyethylene terephthalate (RT 543C,produced by Nihon Unipet K.K.) in the same way as in Example 22. Theoxygen permeability of the bottle obtained was measured 0.34cc/bottle·day·atm.

COMPARATIVE EXAMPLE 11

A preform for a bottle was produced by injection molding by using 10parts of the copolymerized polyester obtained in Example 8. The preformwas formed into a stretched bottle having an inner volume of 1.5 l by abiaxial orientation blowing machine. The configuration of the bottleobtained was irregular and the mechanical strength thereof was low.

As is clear from the above Examples and Comparative Examples, acopolymerized polyester composition of the present invention, anoriented molded product thereof and a hollow container producedtherefrom exhibit better gas barrier property than a polyethyleneterephthalate itself or a blend of a polyethylene terephthalate and apolyethylene isophthalate, and a copolymerized polyester of the presentinvention is therefore suitable as a packaging material which isrequired to have a high gas barrier property.

EXAMPLE 24

97 parts of dimethylisophthalate, 18 parts of dimethyl-2,6-naphthalenedicarboxylate, 71 parts of ethylene glycol and 0.03 part of manganeseacetate tetrahydrate were charged into a reaction vessel and weresubjected to ester exchange reaction while gradually raising thetemperature from 160° C. to 230° C. until there was no effluent.

To the reaction system, 32 parts of 1,3-phenylenedi(oxyacetic acid),0.02 part of orthophosphoric acid and 0.03 part of germanium dioxidewere added in that order. The pressure of the polymerizer was graduallyreduced from ordinary pressure to 1 Torr and the temperature wasgradually raised from 230° C. to 260° C., and after 4.5-hourpolymerization in total, a highly transparent polyester having anintrinsic viscosity of 0.67 was obtained.

EXAMPLE 25

Polymerization was carried out in the same way as in Example 24 exceptthat 82 parts of dimethylisophtalate, 34 parts ofdimethyl-2,6-naphthalene dicarboxylate, 70 parts of ethylene glycol and32 parts of 1,3-phenylenedi(oxyacetic acid) were used. The intrinsicviscosity of the polymer obtained was 0.64.

EXAMPLE 26

Polymerization was carried out in the same way as in Example 24 exceptthat 66 parts of dimethylisophthalate, 50 parts ofdimethyl-2,6-naphthalene dicarboxylate, 68 parts of ethylene glycol and31 parts of 1,3-phenylenedi(oxyacetic acid) were used. The intrinsicviscosity of the polymer obtained was 0.60.

EXAMPLE 27

Polymerization was carried out in the same way as in Example 24 exceptthat 81 parts of dimethylisophthalate, 17 parts ofdimethyl-2,6-naphthalene dicarboxylate, 61 parts of ethylene glycol and47 parts of 1,3-phenylenedi(oxyacetic acid) were used. The intrinsicviscosity of the polymer obtained was 0.61.

EXAMPLE 28

Polymerization was carried out in the same way as in Example 24 exceptthat 66 parts of dimethylisophthalate, 33 parts ofdimethyl-2,6-naphthalene dicarboxylate, 59 parts of ethylene glycol and46 parts of 1,3-phenylenedi(oxyacetic acid) were used. The intrinsicviscosity of the polymer obtained was 0.60.

EXAMPLE 29

Polymerization was carried out in the same way as in Example 24 exceptthat 45 parts of dimethylisophthalate, 23 parts ofdimethyl-2,6-naphthalene dicarboxylate, 22 parts ofdimethyl-4,4'-biphenyldicarboxylate, 50 parts of ethylene glycol and 32parts of 1,3-phenylenedi(oxyacetic acid) were used. The intrinsicviscosity of the polymer obtained was 0.63.

The polyester resins obtained in Examples 24 to 29 and ComparativeExample were extruded into sheets of about 200 μm thick and the oxygenpermeabilities thereof were measured. The results are collectively shownin Table 4.

                  TABLE 4                                                         ______________________________________                                               Dicarboxylic acid                                                             (mol % in acid                                                                component)                 Tg                                                 IPA.sup.( *.sup.1)                                                                  PDDA.sup.( *.sup.2)                                                                     NDCA.sup.( *.sup.3)                                                                     PO.sub.2.sup.( *.sup.4)                                                              (°C.)                          ______________________________________                                        Example 24                                                                             70      20        10      0.38   52                                  Example 25                                                                             60      20        20      0.42   57                                  Example 26                                                                             50      20        30      0.46   60                                  Example 27                                                                             60      30        10      0.28   50                                  Example 28                                                                             50      30        20      0.32   53                                  Example 29                                                                             42      26        17      0.48   58                                  (*5)                                                                          ______________________________________                                         [Notes                                                                        .sup.(*.sup.1) IPA: isophthalic acid                                          .sup.(*.sup.2) PDDA: 1,3phenylenedi(oxyacetic acid)                           .sup.(*.sup.3) NDCA: 2,6naphthalene dicarboxylic acid                         .sup.(*.sup.4) PO.sub.2 : oxygen permeability, cc · mm/m.sup.2       · day · atm.                                                (*5): containing 15 mol % of 4,4biphenyldicarboxylic acid based on the        total acid component                                                     

As is clear from Table 4, a copolymerized polyester of the presentinvention has achieved a lower gas permeability than that ofpolyethylene isophthalate without extremely lowering the Tg (Tg≧50° C.),and a copolymerized polyester of the present invention is thereforesuitable as a gas barrier material.

EXAMPLE 30

20 parts of the copolymerized polyester obtained in Example 28 were dryblended with 80 parts of a polyethylene terephthalate (RT 543C, producedby Nihon Unipet K.K.), and the blend was formed into a preform for abottle by injection molding. The preform was formed into a stretchedbottle having an inner volume of 1.5 l by a biaxial orientation blowingmachine. The average wall thickness of the shoulder portion and the bodyportion was 0.33 mm and the total surface area was 700 cm². The oxygenpermeability of the bottle obtained was measured 0.22 cc/bottle·day·atm.

COMPARATIVE EXAMPLE 12

A stretched bottle having an inner volume of 1.5 l was formed by using apolyethylene terephthalate (RT 543C, produced by Nihon Unipet K.K.)solely in the same way as in Example 30. The oxygen permeability of thebottle obtained was measured 0.43 cc/bottle·day·atm.

EXAMPLE 31

52 parts of dimethylisophthalate, 60 parts of 1,3-phenylenedi(oxyaceticacid), 32 parts of dimethyl-2,6-naphthalene dicarboxylate, 49 parts ofethylene glycol and 0.03 part of titanium tetrabutoxide were chargedinto a reaction vessel and were subjected to ester exchange reactionwhile gradually raising the temperature from 200° C. to 230° until therewas no effluent.

The pressure of the polymerizer was gradually reduced from ordinarypressure to 1 Torr and the temperature was gradually raised from 230° C.to 260° C., and after 5.0-hour polymerization in total, a highlytransparent polyester having an intrinsic viscosity of 0.67 wasobtained.

EXAMPLE 32

Polymerization as carried out in the same way as in Example 31 exceptthat 38 parts of dimethylisophthalate, 59 parts of1,3-phenylenedi(oxyacetic acid), 48 parts of dimethyl-2,6-naphthalenedicarboxylate and 48 parts of ethylene glycol were used. The intrinsicviscosity of the polymer obtained was 0.64.

EXAMPLE 33

Polymerization was carried out in the same way as in Example 31 exceptthat 25 parts of dimethylisophthalate, 72 parts of1,3-phenylenedi(oxyacetic acid), 46 parts of dimethyl-2,6-naphthalenedicarboxylate and 39 parts of ethylene glycol were used. The intrinsicviscosity of the polymer obtained was 0.61.

EXAMPLE 34

Polymerization was carried out in the same way as in Example 31 exceptthat 24 parts of dimethylisophthalate, 85 parts of1,3-phenylenedi(oxyacetic acid), 31 parts of dimethyl-2,6-naphthalenedicarboxylate and 31 parts of ethylene glycol were used. The intrinsicviscosity of the polymer obtained was 0.63.

EXAMPLE 35

Polymerization was carried out in the same way as in Example 31 exceptthat 17 parts of dimethylisophthalate, 58 parts of1,3-phenylenedi(oxyacetic acid), 21 parts of dimethyl-2,6-naphthalenedicarboxylate and 20 parts of ethylene glycol were used. The intrinsicviscosity of the polymer obtained was 0.64.

COMPARATIVE EXAMPLE 13

Polymerization was carried out in the same way as in Example 31 exceptthat 52 parts of dimethylisophthalate, 99 parts ofdimethyl-2,6-naphthalene dicarboxylate and 84 parts of ethylene glycolwere used. The intrinsic viscosity of the polymer obtained was 0.68.

The polyester resins obtained in Examples 31 to 35 and ComparativeExample 13 were extruded into sheets of about 200 μm thick and theoxygen permeabilities thereof were measured. The results arecollectively shown in Table 5.

                  TABLE 5                                                         ______________________________________                                               Dicarboxylic acid                                                             (Mol % in acid component)  Tg                                                 IPA.sup.( *.sup.1)                                                                  PDDA.sup.( *.sup.2)                                                                     NDCA.sup.( *.sup.3)                                                                     PO.sub.2.sup.( *.sup.4)                                                              (°C.)                          ______________________________________                                        Example 31                                                                             40      40        20      0.22   49                                  Example 32                                                                             30      40        30      0.24   52                                  Example 33                                                                             20      50        30      0.18   48                                  Example 34                                                                             20      60        20      0.15   45                                  Example 35                                                                             17      51        17      0.24   50                                  (*5)                                                                          Comparative                                                                            40       0        60      0.85   86                                  Example 13                                                                    ______________________________________                                         [Notes                                                                        .sup.(*.sup.1) IPA: isophthalic acid                                          .sup.(*.sup.2) PDDA: 1,3phenylenedi(oxyacetic acid)                           .sup.(*.sup.3) NDCA: 2,6naphthalenedicarboxylic acid                          .sup.(*.sup.4) PO.sub.2 : oxygen permeability, cc · mm/m.sup.2       · day · atm.                                                (*5): Containing 15 mol % of 4,4biphenyldicarboxylic acid based on the        total acid component                                                     

As is clear from Table 5, a copolymerized polyester of the presentinvention has achieved a lower gas permeability than that of apolyethylene isophthalate without extremely lowering the Tg (Tg≧40° C.),and a copolymerized polyester of the present invention is thereforesuitable as a gas barrier material.

EXAMPLE 36

10 parts of the copolymerized polyester obtained in Example 34 were dryblended with 90 parts of a polyethylene terephthalate (RT 543C, producedby Nihon Unipet K.K.), and the blend was formed into a preform for abottle by injection molding. The preform was formed into a stretchedbottle having an inner volume of 1.5 l by a biaxial orientation blowingmachine. The average wall thickness of the shoulder portion and the bodyportion was 0.33 mm and the total surface area was 700 cm². The oxygenpermeability of the bottle obtained was measured 0.20 cc/bottle·day·atm.

COMPARATIVE EXAMPLE 14

A stretched bottle having an inner volume of 1.5 l was formed by using apolyethylene terephthalate (RT 543C, produced by Nihon Unipet K.K.)solely in the same way as in Example 36. The oxygen permeability of thebottle obtained was measured 0.43 cc/bottle·day·atm.

COMPARATIVE EXAMPLE 15

A stretched bottle having an inner volume of 1.5 l was formed by using10 parts of the polyethylene isophthalate obtained in ComparativeExample 4 and 90 parts of a polyethylene terephthalate (RT 543C,produced by Nihon Unipet K.K.) in the same way as in Example 36. Theoxygen permeability of the bottle obtained was measured 0.37cc/bottle·day·atm.

EXAMPLE 37

A three-layered hollow container was produced by a multi-layered hollowcontainer molding machine (Nissei ASB 50TH) in such a manner that thecopolymerized polyester obtained in Example 8 for an intermediate layerconstituted the intermediate layer and a polyethylene terephthalate (RT543C, produced by Nihon Unipet K.K., glass transition point (Tg): 72°C.) constituted the outer and the inner layers. The cylinder temperaturewas set at 270° C. on the polyethylene terephthalate side, and at 245°C. at the copolymerized polyester side. A preform was formed at a moldtemperature of 10° C. by injection molding and the preform obtained wasformed into a hollow container having an inner volume of 500 cc by blowstretching at a surface temperature of 95° C. The total length of thehollow container obtained was 183 mm, the outer diameter of the bodyportion was 73 mm and the wall thickness of the body portion was 300 μm.No ply separation was observed.

The content of the copolymerized polyester in the container and theoxygen permeability of the container are shown in Table 6.

EXAMPLE 38

A multi-layered hollow container was produced by using the copolymerizedpolyester obtained in Example 9 and the polyethylene terephthalate inthe same way as in Example 37. The oxygen permeability of the containerobtained is shown in Table 6.

EXAMPLE 39

Three kinds of multi-layered hollow containers were produced by usingthe copolymerized polyester obtained in Example 12 and the polyethyleneterephthalate in the same way as in Example 37 while varying the contentof the copolymerized polyester in the container. The oxygen permeabilityof the containers obtained are shown in Table 6.

EXAMPLE 40

A multi-layered hollow container was produced by using the copolymerizedpolyester obtained in Example 13 and the polyethylene terephthalate inthe same way as in Example 37. The oxygen permeability of the containerobtained is shown in Table 6.

EXAMPLE 41

A multi-layered hollow container was produced by using the copolymerizedpolyester obtained in Example 14 and the polyethylene terephthalate inthe same way as in Example 37. The oxygen permeability of the containerobtained is shown in Table 6.

EXAMPLE 42

Two kinds of multi-layered hollow containers were produced by using thecopolymerized polyester obtained in Example 15 and the polyethyleneterephthalate in the same way as in Example 37 while varying the contentof the copolymerized polyester in the container. The oxygen permeabilityof the container obtained is shown in Table 6.

COMPARATIVE EXAMPLE 16

A single-layered bottle consisting of a polyethylene terephthalate (RT543C, produced by Nihon Unipet K.K.) was produced in the same way as inExample 37. The oxygen permeability of the container obtained is shownin Table 6.

COMPARATIVE EXAMPLE 17

A multi-layered hollow container was produced in the same way as inExample 37 except for using the polyethylene isophthalate obtained inComparative Example 4 in place of the copolymerized polyester. Theoxygen permeability of the container obtained is shown in Table 6.

                  TABLE 6                                                         ______________________________________                                        Oxygen Permeability of Polyester Multi-Layered                                Hollow Container                                                                        Copolymerized polyester                                                                 wt % in                                                             Raw Material                                                                            container PO.sub.2.sup.(1)                                ______________________________________                                        Example 37  Example 8   20        0.10                                        Example 38  Example 9   20        0.15                                        Example 39  Example 12  10        0.15                                                                20        0.11                                                                40        0.07                                        Example 40  Example 13  20        0.08                                        Example 41  Example 14  20        0.05                                        Example 42  Example 15   5        0.12                                                                20        0.04                                        Comparative  --          0        0.25                                        Example 16                                                                    Comparative Comparative 20        0.18                                        Example 17  Example 4   40        0.15                                        ______________________________________                                         [Note                                                                         .sup.(1) PO.sub.2 : oxygen permeability, cc/bottle · day             · atm. value obtained by correcting the amount of oxygen             permeated in air by the percentage (21%) of oxygen.                      

As is clear from the above Examples and Comparative Examples, apolyester multi-layered hollow container of the present inventionexhibits a better gas barrier property than a single-layered containerof a polyethylene terephthalate or a multi-layered container of apolyethylene terephthalate and a polyethylene isophthalate. In addition,since use of a small amount of copolymerized polyester, as compared witha polyethylene terephthalate, produces a container having a good gasbarrier property, the mechanical strength and the heat resistance whicha polyethylene terephthalate container intrinsically has are notimpaired. Thus, a polyester multi-layered hollow container of thepresent invention is suitable as a container which is required to have ahigh gas barrier property.

What is claimed is:
 1. A polyester produced by copolymerizing adicarboxylic acid component A comprisinga. 10 to 90 mol % of isophthalicacid or an ester forming derivative thereof, b. 10 to 60 mol % of aphenylenedi(oxyacetic acid) represented by the formula [I]: ##STR15##wherein R¹, R² R³ and R⁴ each represent a hydrogen atom, an alkyl grouphaving 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms,a phenyl group, a chlorine atom, a bromine atom or a fluorine atom, oran ester forming derivative thereof; and c. 0 to 45 mol % of anaphthalenedicarboxylic acid or an ester forming derivative thereof, anda diol component B.
 2. A polyester according to claim 1, which has anintrinsic viscosity of 0.4 to 2.0 as measured at 30° C. in a mixedsolvent of phenol and tetrachloroethane in a weight ratio of 1:1.
 3. Apolyester according to claim 1, wherein said phenylenedi(oxyacetic acid)represented by the formula [I] is one member selected from the groupconsisting of 1,2-phenylenedi(oxyacetic acid), 1,3-phenylenedi(oxyaceticacid), 1,4-phenylenedi(oxyacetic acid),2-methyl-1,3-phenylenedi(oxyacetic acid),5-methyl-1,3-phenylenedi(oxyacetic acid),4-methyl-1,3-phenylenedi(oxyacetic acid),5-ethyl-1,3-phenylenedi(oxyacetic acid),4-ethyl-1,3-phenylenedi(oxyacetic acid),5-methoxy-1,3-phenylenedi(oxyacetic acid),4-methoxy-1,3-phenylenedi(oxyacetic acid),4-chloro-1,2-phenylenedi(oxyacetic acid) and4-chloro-1,3-phenylenedi(oxyacetic acid).
 4. A polyester according toclaim 1, wherein said naphthalenedicarboxylic acid is one memberselected from the group consisting of 1,4-naphthalenedicarboxylic acid,1,5-naphthalenedicarboxylic acid, 1,8-naphthalenedicarboxylic acid,2,3-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, and2,7-naphthalenedicarboxylic acid.
 5. A polyester according to claim 1,wherein said diol component B is one member selected from the groupconsisting of ethylene glycol, 1,2-propanediol, 1,3-propanediol,1,4-butanediol, pentamethylene glycol, hexamethylene glycol, neopentylglycol, cyclohexanedimethanol, diethylene glycol, Bisphenol A andBisphenol D.
 6. A polyester according to claim 1, wherein saiddicarboxylic acid component A comprisesa. 40 to 90 mol % of isophthalicacid or an ester forming derivative thereof, and b. 10 to 60 mol % of aphenylenedi(oxyacetic acid) represented by the formula [I] or an esterforming derivative thereof.
 7. A polyester according to claim 1, whereinsaid dicarboxylic acid component A comprisesa. 50 to 85 mol % ofisophthalic acid or an ester forming derivative thereof, b. 10 to 45 mol% of a phenylenedi(oxyacetic acid) represented by the formula [I] or anester forming derivative thereof, and c. 5 to 40 mol % of naphthalenedicarboxylic acid or an ester forming derivative thereof.
 8. A polyesteraccording to claim 1, wherein said dicarboxylic acid component Acomprisesa. 10 to 50 mol % of isophthalic acid or an ester formingderivative thereof, b. 20 to 60 mol % of a phenylenedi(oxyacetic acid)represented by the formula [I] or an ester forming derivative thereof,and c. 10 to 45 mol % of naphthalenedicarboxylic acid or an esterforming derivative thereof, the molar ratio of said component b and saidcomponent c being 50:50 to 80:20.
 9. A packaging material produced froma polyester according to claim 1.